1. Field of Invention
The present invention relates to a gas generator for a restraining device such as an airbag apparatus installed on a vehicle.
2. Description of Related Art
Among gas generators used in airbag apparatuses installed on vehicles, in a pyrotechnic gas generator, a gas generating agent serving as a gas generation source is accommodated inside a housing which corresponds to an outer container.
When the gas generating agent burns and high-temperature gas is generated during actuation, the gas is ejected out of a gas discharge port formed in the housing, and the airbag is inflated and deployed. In this process, the housing is strong enough to withstand the increased internal pressure.
However, for some reason, the gas generator may burn abnormally and an excess pressure that exceeds the designed strength may be applied to the housing. Even if the housing is broken as the result thereof, such an abnormal situation that the occupant is injured by the fractured housing has to be avoided.
WO-A No. 94/25315 discloses dealing with such an abnormal situation.
In the gas generator shown in FIG. 1 of WO-A No. 94/25315, an igniter 18 is accommodated inside an igniter support tube 30 disposed inside a housing 12.
The tube 30 is fixed to both end surfaces (bottom surface and top surface) of the housing 12, and a plurality of apertures (flame-transferring holes) 40 are formed on the wall 34 side. In FIG. 1, a total of 13 apertures 40 are shown, and therefore it can be found that at least 26 apertures are formed along the entire circumference of the tube 30.
FIG. 2 of WO-A 94/25315 shows a state after the gas generator shown in FIG. 1 has been actuated (state in which an excess pressure caused by abnormal combustion has been applied). The housing 12 undergoes expansion and deformation such as to protrude toward a wall 34, and the tube 30 is broken in the portion where the apertures 40 are formed.
The portion of the tube 30 where the apertures 40 are formed thus serves as a reduced strength portion, and consequently, when an excess pressure is applied inside the housing 12, the tube 30 is broken, the inner volume is increased, and the internal pressure is then decreased, thereby preventing the housing 12 from fracturing.
The housing strength is increased by the wall 34 concaved inwardly. The joining surface area of a flare portion 31 of the tube 30 is made larger.